This invention relates to polyurethane polymers, particularly polyurethane polymers containing dispersed reinforcing agents.
It is well known to reinforce polyurethane polymers with macroscopic fillers such as glass, polyamide, polyester, graphite or similar fibers; particulate fillers such as calcium carbonate, barium sulfate and the like, and other fillers such as sand, and milled or flaked glass. Although these fillers are known to improve the properties of the polyurethane, they have several drawbacks. One is the amount of such fillers which are needed to obtain good reinforcement. Typically, up to about 60 percent or more of the filled polymer comprises the filler material. It would be highly desirable to obtain good reinforcement at lower levels of filler. Another problem is that many of these filler materials do not strongly adhere to the polyurethane matrix. Accordingly, the reinforcement is not as great as would be expected. Another problem is that although certain properties such as stiffness and tensile strength are improved by the use of these fillers, these improvements are usually accompanied by a substantial decrease in other properties, notably impact strength, fatigue and elongation.
It is also known to reinforce a polyurethane polymer by using a polyol containing colloidally dispersed polymer particles. These so-called "polymer polyols" generally contain as the dispersed polymer a styrene/acrylonitrile copolymer, a polyurea polymer or a polyurethaneurea polymer. The dispersed polymers are usually prepared in situ by polymerizing the appropriate monomers within the polyol. The reinforced polyurethane is prepared by reacting the dispersion with a polyisocyanate. The use of polymer polyols has not been found to significantly increase properties such as tensile strength or flexural modulus. The major use for these products has been in flexible polyurethane foams, where the dispersed particles increase the load bearing properties of the foam, and perform a cell opening function.
It would be desirable to provide a reinforced polyurethane in which good reinforcement is obtained even at relatively low filler levels and in which desirable improvements in physical properties are achieved without major losses in other properties.